private static bool MakeLeanMSG3(Store msg, ResSet predicates, StatementSink removed,
ResSet nodesremoved, SyncPath path) {
// The variable path has to be expanded by including the statements
// connected to the variables on the frontier. Statements
// mentioning a variable node have already been considered.
// The target of each such statement can be considered fixed
// or variable. If a variable is considered fixed, the edge
// must exist in the MSG substituting the variables for their
// values. If it's variable, it has to have at least one
// match in the MSG but not as any of the variable nodes.
// If all targets are considered fixed (and have matches),
// then the variables so far (and their edges) can all be
// removed and no more processing needs to be done.
// There are (2^N)-1 other considerations. For each of those,
// the targets considered variables all become the new
// frontier, and this is repeated.
// First, get a list of edges from the frontier that we
// haven't considered yet.
ArrayList alledges = new ArrayList();
foreach (BNode b in path.FrontierVariables) {
// Make sure all edges are kept because even the ones
// to literals have to be removed when duplication is found.
foreach (Statement s in msg.Select(new Statement(b, null, null)))
alledges.Add(new Edge(true, b, s.Predicate, s.Object));
foreach (Statement s in msg.Select(new Statement(null, null, b)))
alledges.Add(new Edge(false, b, s.Predicate, s.Subject));
}
ArrayList newedges = new ArrayList();
ResSet alltargets = new ResSet();
ResSet fixabletargetsset = new ResSet(); // can be fixed
ResSet variabletargetsset = new ResSet(); // must be variable
foreach (Edge e in alledges) {
if (path.Path.ContainsKey(e)) continue;
path.Path[e] = e;
// This checks if we can keep the target of this edge
// fixed, given the variable mappings we have so far.
bool isTargetFixable =
msg.Contains(e.AsStatement().Replace(path.Mapping));
// If the target of e is any of the following, we
// can check immediately if the edge is supported
// by the MSG under the variable mapping we have so far:
// a named node, literal, fixed node, or predicate
// a variable we've seen already
// If it's not supported, this path fails. If it is
// supported, we're done with this edge.
if (!(e.End is BNode)
|| path.FixedNodes.Contains(e.End)
|| predicates.Contains(e.End)
|| path.VariableNodes.Contains(e.End)) {
if (!isTargetFixable) return false;
continue; // this edge is supported, so we can continue
}
// The target of e is a new BNode.
// If this target is not fixable via this edge, it's
// not fixable at all.
if (!isTargetFixable) {
fixabletargetsset.Remove(e.End);
variabletargetsset.Add(e.End);
}
if (!alltargets.Contains(e.End)) {
alltargets.Add(e.End);
fixabletargetsset.Add(e.End);
}
newedges.Add(e);
}
// If all of the targets were fixable (trivially true also
// if there simple were no new edges/targets), then we've reached
// the end of this path. We can immediately remove
// the edges we've seen so far, under the variable mapping
// we've chosen.
if (variabletargetsset.Count == 0) {
foreach (Edge e in path.Path.Keys) {
Statement s = e.AsStatement();
msg.Remove(s);
if (removed != null) removed.Add(s);
}
foreach (Entity e in path.Mapping.Keys)
nodesremoved.Add(e);
return true;
}
// At this point, at least one target must be a variable
// and we'll have to expand the path in that direction.
// We might want to permute through the ways we can
// take fixable nodes as either fixed or variable, but
// we'll be greedy and assume everything fixable is
// fixed and everything else is a variable.
path.FixedNodes.AddRange(fixabletargetsset);
path.VariableNodes.AddRange(variabletargetsset);
// But we need to look at all the ways each variable target
// can be mapped to a new value, which means intersecting
// the possible matches for each relevant edge.
Entity[] variables = variabletargetsset.ToEntityArray();
ResSet[] values = new ResSet[variables.Length];
Entity[][] values_array = new Entity[variables.Length][];
int[] choices = new int[variables.Length];
for (int i = 0; i < variables.Length; i++) {
foreach (Edge e in newedges) {
if (e.End != variables[i]) continue;
// Get the possible values this edge allows
Resource[] vr;
if (e.Direction)
vr = msg.SelectObjects((Entity)path.Mapping[e.Start], e.Predicate);
else
vr = msg.SelectSubjects(e.Predicate, (Entity)path.Mapping[e.Start]);
// Filter out literals and any variables
// on the path! The two paths can't intersect
// except at fixed nodes.
ResSet v = new ResSet();
foreach (Resource r in vr) {
if (r is Literal) continue;
if (path.Mapping.ContainsKey(r)) continue;
v.Add(r);
}
// Intersect these with the values we have already.
if (values[i] == null)
values[i] = v;
else
values[i].RetainAll(v);
// If no values are available for this variable,
// we're totally done.
if (values[i].Count == 0) return false;
}
choices[i] = values[i].Count;
values_array[i] = values[i].ToEntityArray();
}
// Now we have to permute through the choice of values.
// Make an array of the number of choices for each variable.
Permutation p = new Permutation(choices);
int[] pstate;
while ((pstate = p.Next()) != null) {
SyncPath newpath = new SyncPath();
newpath.FixedNodes.AddRange(path.FixedNodes);
newpath.VariableNodes.AddRange(path.VariableNodes);
newpath.Mapping = (Hashtable)path.Mapping.Clone();
newpath.Path = (Hashtable)path.Path.Clone();
newpath.FrontierVariables = variabletargetsset;
for (int i = 0; i < variables.Length; i++) {
Entity value = values_array[i][pstate[i]];
newpath.Mapping[variables[i]] = value;
newpath.FixedNodes.Add(value);
}
if (MakeLeanMSG3(msg, predicates, removed,
nodesremoved, newpath)) return true;
}
return false;
}
